More specifically, the present invention relates to a plant for producing aircraft transmission gears. As is known, after being cut, aircraft gears undergo surface hardening, which, depending on the application, comprises carburizing or nitriding; after which, the gears undergo further processing and, normally, a finish machining operation, e.g. grinding.
To obtain gears of a given uniform surface strength, specimen carburized or nitrided gears are checked to determine the effective carburized or nitrided case depth of each specimen at various points as specified in a given quality control protocol. That is, after heat treating, specimen gears are taken off the production line and sectioned, and the effective carburized or nitrided case depths of the sectioned parts are determined at the specified points in known manner.
Alternatively, a predetermined number of test pieces are also produced alongside the gears and hardened in the same way, and, like the gears, are sectioned to determine the effective carburized/nitrided case depth.
Though universally adopted, the above known effective case depth checking method is unsatisfactory in various respects, foremost of which is the destructive nature of the method, which calls for sectioning both test pieces and gears. Moreover, it involves expense in terms of wastage of heat treated material, and, in particular, additional expense when using test pieces, and loss-of-production expense when sectioning actual gears.
Moreover, both test pieces and specimen gears are sectioned and measured at dedicated off-line stations, which means additional transfer and handling costs.
Finally, random specimen checks are no guarantee of the quality of production as a whole, and do not rule out the possibility of below-standard gears eventually being installed in, and so unacceptably impairing the efficiency and reliability of, the transmission.